In recent years, insulating materials composed of a polymeric material have been used in semiconductors, IC, hybrid IC, printed circuit boards, display elements, display parts and the like as overcoats such as passivation films, solder resists, plating resists, layer insulation films and moistureproof protective films, and the like. The polymeric materials used in these applications have come to be required to have improved properties and high reliability according to the miniaturization of electronic parts (including components and devices), the high density assembly (high integration) and speeding up of semiconductors, and the like.
For example, a passivation film is used for preventing moisture and/or impurities from infiltrating into a semiconductor element. Since a material for passivation becomes a component of the semiconductor element, it is required to be good in heat resistance, low water-absorption property, electrical insulating property, adhesion to a substrate or the like, etc. As materials for passivation, heat-resistant polymeric materials such as polyimide resins are used together with inorganic materials such as silicon dioxide. Among these polymeric materials, polymeric materials excellent in, particularly, heat resistance and flexibility are used not only as passivation materials, but also as layer insulation films for multilayer interconnection in semiconductor elements or printed circuit boards. Since a difference in level between wiring layers, which is caused by the multilayer interconnection attendant upon high integration, causes the disconnection of wiring layers such as aluminum wires, there has been demand for development of a layer insulation film formed of a polymeric material and having good level-difference covering ability (step coverage property).
The solder resist is a resist which is silk-screened so as to protect a surface pattern on a printed board and at the same time to expose only mounting holes and electrical input-output terminals for parts (including devices and components) and is used for applying a solder to the exposed areas only to fix the parts thereto. Since the solder resist remains as a permanent coating film on the printed board, it is required to be excellent in adhesion to the surface of a copper foil, suitability for screen printing, electrical insulating property, soldering heat resistance, solvent resistance and the like. Epoxy resins have heretofore been principally used as materials for solder resists.
As described above, the polymeric materials used as insulating materials are required to be excellent in heat resistance, solvent resistance, low water-absorption property (moisture resistance), electrical insulating property, adhesion, chemical resistance and the like. However, the polymeric materials used as insulating materials to date (up to the present) have not sufficiently satisfied these properties. For example, epoxy resins and polyimide resins are excellent in heat resistance but insufficient in moisture resistance. Polybutadiene resins similarly used as insulating materials are excellent in moisture resistance but insufficient in heat resistance. Besides, as polymeric materials used in applications such as solder resists and plating resists, photosensitive polymeric resists capable of conducting minute processing are demanded in addition to non-photosensitive polymeric resists on which a pattern is printed by the conventional screen printing in order to cope with the high integration density of assembly of semiconductors.
By the way, cycloolefin resins such as thermoplastic norbornene resins have heretofore been known as polymeric materials having good electrical insulating property. However, the conventional cycloolefin resins have involved shortcomings such as (i) insufficient heat resistance because they are thermoplastic resins, (ii) poor adhesion to inorganic materials such as silicon and (iii) insufficient solvent resistance, and have not had properties satisfactory for insulating materials such as layer insulation films. For example, when a cycloolefin resin insufficient in solvent resistance is used as a layer insulation film in the form of plural layers such as multilayer interconnection (wiring) structures, the lower layer insulation film is attacked by a solvent upon formation of the upper layer insulation film by a coating process.
It has heretofore been proposed to improve the heat resistance and solvent resistance of an addition copolymer of a norbornene type monomer with ethylene by using a crosslinking agent such as sulfur or an organic peroxide, or irradiating an ionizing radiation such as an electron ray (Japanese Patent Application Laid-Open No. 34924/1987). However, this process involves a shortcoming that sulfur remains, the storage stability of a formulated solution is poor, or plant and equipment investment requires an enormous cost.